Heat stress: How much does it drain your pigs and profits?

Most people in the pork industry know the toll heat stress takes on pigs: reduced performance, a compromised gastrointestinal system, chronic disease, reduced feed intake and higher mortality rates.
calendar icon 18 June 2018
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Less known are the staggering financial losses wrought by heat stress on producers and the pork industry in general. Each year, heat stress costs US pig farmers about $900 million in revenues — about twice the amount lost as a result of the porcine reproductive and respiratory syndrome virus, according to an estimate by Steven Pollmann, PhD, a livestock consultant and former president of western operations for Murphy-Brown LLC, a division of Smithfield Foods.

These losses include impaired sow productivity as well as losses from grow-finish pigs. Pollmann estimates that on average producers lose $50 to $60 per animal each year due to heat stress.1

Since pigs lack the ability to sweat, they are extremely sensitive to heat. They become susceptible to heat stress at about 70° F (21° C). If temperatures stay at 80° F (27° C) or higher for several days, it could have a myriad of negative effects on breeding herds, sows and those at the grow-finish stage of production. Under such high temperatures, pigs also experience reductions in performance.

“Heat stress is far and away the single biggest loss we see,” Pollmann says. “It will have more impact on the industry than disease because it hits every farm. Heat stress, particularly in the North American market, will hit 95% of the herds.”

“It affects all of our producers regardless of geographic location,” adds Chris Hostetler, director of animal science for the National Pork Board. “It results in a loss of productivity of 10%. That’s pretty substantial — a 10% loss of productivity for 5 months of the year. If we could mitigate it, it would make a big difference.”

Seasonal infertility and reduced growth

Heat stress hits producers in the pocketbook in two key areas: seasonal infertility and reduced growth.

Breeding herds are particularly susceptible to an array of reproductive issues, including decreased farrowing rates, smaller numbers born per litter, a reduced number of piglets born alive per litter, higher embryonic deaths during early gestation, a larger number of stillborn piglets and miscarriages. Heat stress is also responsible for increased mortality among sows.

Not only are the sows “more likely to abort but they are less likely to conceive in the first place,” says Lance Baumgard, a professor in the department of animal science at Iowa State University.

This reduced fertility rate brought on by heat stress forces many producers to prematurely cull their sows, Hostetler says. As a result, many farmers fail to get the full value of what they’ve invested in the animal, he says.

Heat stress affects the potency of males as well. Despite the fact that most boar studs are housed in air-conditioned pens these days, there is typically an increase in the disposal of collected semen during the hot months, Hostetler says.

Lifelong impact on piglets

And the estimated economic loss to producers does not include the lifelong impact on piglets born during these hot months, Baumgard says. Piglets born to heat-stressed sows become fatter and have a higher body temperature their whole lives, he says.

“That’s important because that thermal energy has to come from feed energy, and that feed is purchased by the farmer,” Baumgard says.

These piglets are also more susceptible to chronic health problems. He figures that if the impact on embryos and piglets is factored in, the loss could probably be twice the $900 million figure.

In addition, heat stress has negative consequences for the meat-processing segment of the pork industry, Baumgard says. Because pigs affected by heat stress tend to make more fat, that has an impact on the quality of certain types of pork made by food processors, such as bacon, he says. Further, pigs marketed during the summer typically have “flimsy” fat, and the Iowa State University research group has discovered that this is because adipose tissue from heat-stressed pigs contains more moisture than during other times of the year.

Heat-stressed pigs are also prone to reduced feed intake. Among sows, that leads to lower milk production, which in turn begets lower-weight piglets.

Reduced growth

Indeed, reduced growth poses another major financial challenge to producers, Baumgard says. When the animal is slow to reach market weight, do you wait or ship it out for sale at a lighter weight?

“This variation in final bodyweight markedly increases during heat stress,” he says.

And younger sows lose weight because they’re not eating enough, Pollmann says.

“So you end up having open sows for about 20 to 30 days because you’re trying to get the bodyweight right and rebuild body reserves,” he says.

Pollmann says that historically many producers have tried to address the problem of underweight, open sows by breeding more sows, a recommendation he says is frequently made by production consultants. But that presents a new set of complications, including the possibility of overcrowding in the pens, he says.

“It’s a really inefficient way of raising pigs,” Hostetler adds.

Biology over engineering

Baumgard says that as the industry evolves so is the thinking on heat stress. Ten or 15 years ago, he says, many believed problems created by heat stress could be resolved chiefly by engineering solutions, such as adequate ventilation and cooling pads. But he says that, in addition to physically modifying the environment, there is a growing recognition that heat stress is primarily a biological issue. He says animal nutritionists could explore the development of rations that help strengthen gut integrity and minimize basal heat production.

And as scientists work to find solutions Pollmann says the principal strategies for tackling heat stress must still apply.

“Make sure the cooling systems are right, that there is enough ventilation and the pens are not overpopulated,” he says.


1. Pollmann, D. S.. Seasonal effects on sow herds: industry experience and management strategies. J Anim Sci. 2010;88(Suppl. 3):9 (Abstr).

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